1. Field of the Invention
The present invention relates to a transmission gear with a dog clutch gear which is to be incorporated into a manual transmission for vehicle use, and to a method of manufacturing a transmission gear with a dog clutch gear.
2. Description of the Related Art
A transmission gear with a dog clutch gear is configured in such a manner that the dog clutch gear is disposed coaxially with the transmission gear. In the past, there was widely used a single body type in which a dog clutch gear and a transmission gear are integrated and in which a tool relief groove which is necessary for cutting of the dog clutch gear is provided between the dog clutch gear and the transmission gear. However, with demand for downsizing, there has been adapted, as a mainstream configuration, a configuration such that no tool relief groove is provided, and the dog clutch gear and the transmission gear are in close contact with each other (hereinafter referred to as a groove-less type). For such a groove-less type, there have been used an integral forging method, and a method in which a dog clutch gear and a transmission gear, formed through forging or cutting, are united together (hereinafter referred to as a combining scheme).
Since the former integral forging method requires an advanced technique, only a few companies, including the applicant of the present application, have succeeded in putting the method to practical use. Therefore, there is no guarantee that the method can be used for manufacture of products even when excellent facilities are provided. Further, as compared with the combining scheme, the integral forging method may involve disadvantages in relation to manufacture of products, depending on product shape. Therefore, the latter combining scheme has still been employed.
In the combining scheme having been employed heretofore, as shown in FIG. 9A, a ring portion 3 of a dog clutch gear 1, which is fitted onto a boss portion 6 of a transmission gear 2, is welded to the boss portion 6 at an interface A between the ring portion 3 and the boss portion 6; or as shown in FIG. 9B, the ring portion 3 and the boss portion 6 are joined together by use of an inner spline 10 formed on the ring portion 3, and an outer spline 10a formed on the boss portion 6.
In the welding type of the conventional combining scheme, since welding can be performed only at a single point; i.e., at the interface A between the ring portion 3 and the boss portion 6, as shown in FIG. 10, base end portions of clutch teeth 4 in close contact with a side surface of the transmission gear 2 are distorted in a warped shape by influence of welding heat, with the result that the base end portions lift from the side surface of the transmission gear.
Further, joining by means of welding tends to cause problems, such as deflection of the center and deterioration of accuracy, which are caused by deformation of the clutch teeth attributed to influence of welding heat. The type in which joining is performed by means of splines involves problems in that forming splines requires a special machining facility, and cost increases due to tool cost. Further, since the clutch teeth 4 are formed integrally with the ring portion 3 on a tooth-by-tooth basis, the element involves a concern about strength.